I think kid C sounds amazing! It takes a lot of courage to stand up to someone who is hitting/punching and get in the middle of a fight! I would be proud if child C was mine!
Wouldn't you want your son to do exactly what he did if it was his little brother on the ground getting hit? I would!
~This is what I have taught ALL my kids:
Never hit anyone first, EVER! ....but if someone hits you, you have our permission to hit them back. And absolutely step in and stop ANYONE from hurting/hitting others...ESPECIALLY your siblings!
*My husband and I agree that we never want any of our kids to be punching bags for anyone...regardless of school policies! I am not naive enough to believe that running and being a tattle-tale will stop a bully from picking on you, if anything it has the potential to make the bullying worse. With all the bullying that happens these days (not that it is new, I had bullys at my schools) I want my kids to stand up for themselves. I would be content with the school punishment but wouldn't punish my child any further for standing up for himself or anyone else. A 'talk' afterward would be sufficient enough.
Asking or telling a child to step away and let their friend or anyone else continue to get a beating while they run and get a teacher is not right, IMHO.
*I have 6 boys, ages 19-5 and so far (knock on some wood) we have not had to deal with any fighting...we've come close but they were handled by them using their brain instead of their muscles!